I personally don't understand it, but for any of us born post 1960, it can be especially troublesome.
Below is a list she calls "trouble spots" in such marriages.
These are points at which cultural differences raise issues and create problems that are either not present or are less severe in monocultural marriages.
Unfortunately they were young at a time where race riots and racial hatred was at its all time high, and that has influenced MANY people of the older generation.
There are many people of that generation who accept it as well..can't hold grudges for things that didn't even affect you, but some people are so reserved and traditionalist that the idea of a mixed couple is disturbing to them.
In terms of other Pros, you can basically look forward to whatever else you enjoy in a relationship with a new person.